Water quality and ecosystem health assessment to define environmental management strategies: case study of Ob and Volga rivers
A comprehensive assessment is presented of the ecotoxicological situation in industry polluted parts of Volga and Ob river's basins from the viewpoint of ecosystem health. Concentrations of organic and inorganic toxic substances in water are reported. Basic clinical and postmortem signs of fish intoxication are described; changes in the cellular structure of their organs and tissues, as well as disturbances in hemogenesis, developing under the effect of toxic agents, are characterized. The comparative characteristics of several microelements (Ni, Cu, Sr, Al, Zn, Co, Mn, Pb, Cd, Hg, As) found in fish are presented. The main disturbances to fish caused by the accumulation of microelements in their organs and tissues are also considered. Based on dose–effect dependencies calculated with respect to the total concentration of toxic substances, standardized to MPC, and fish health criteria, cases that exceed the critical levels of pollutants are demonstrated for the investigated river sections. Our results show that water quality and living conditions for aquatic species in polluted parts of Volga and Ob rivers are unsatisfactory. Based on the prevalence of signs of intoxication in fish, we can conclude that the ecosystem health conditions are quite dramatic and give a clear signal of the need to decrease toxic pollution.
The main question for environmental management is the level to which pollution loading must be reduced to achieve reference conditions and to preserve ecosystem health. To answer this question, we solved to accomplish three tasks :
- Determinate how hydro-chemical information on water quality can be interpreted in terms of a unified parameter, which could reflect the real impacts of the dose taking into account contaminant complexes (multi-pollution);
- Assign criteria for ecosystem health that informatively reflect the impacts of pollution;
- Determine critical levels of water pollution and required load reductions based on a dose–effect relationship.
An integrated impact dose. In rivers and reservoirs, aquatic organisms are exposed to a mixture of all toxicants. It is important to find a numerical parameter describing the total toxic impact on fish. The integrated impact dose of contaminants is determined by their number, concentration and toxic properties. The values of GC or MPC differ by country, in spite of the fact that experimental research techniques to establish the MPCs are universal. For example, in Russia, the MPC values for Cu, V, Mn and some other elements are underestimated, whereas the MPCs for Cd, As, Pb, and Al are overestimated. However, despite these criticisms of the system of MPC, we used data on the toxicological properties of each toxicant based on the MPC adopted in Russia. We have defined the integrated impact dose by summing the excess of real concentration for each of metals with their MPC as follows:
Itox-1 = å(Ci /MPCfishery.).
Itox is the integrated toxicity index; Ci are concentrations registered in water; MPCfishery are MPC for toxic substances accepted in Russia for aquatic life. According to Russian rules of water protection, the water quality may be considered good if Itox is no more than one (0 <Itox-1 ≤1).
Criteria of ecosystem health are the key aspects in the system of estimating critical levels of water contamination and water resource management. Fish health as an indicator of ecosystem health can be determined using methods such as clinical and postmortem examination, and histological, hematological, or biochemical studies. Determination of the critical levels of water contamination requires numerical biological criteria, which also adequately reflect the effect of toxic substances in the water. The following biological parameters were used as criteria for fish and ecosystem health (the average weighted for individual river sections): i) the percentage of fish in which the second or third stages of diseases were diagnosed; ii) the Z-index defined above; iii) the percentage of fish with hemoglobin concentration below 90 g/l and the low levels of neutrophils in the blood, etc.
Dose–effect dependencies and critical levels. Basing on dose–effect dependencies (between numerical indices of fish health and the chemical parameters of water quality, in particular the total concentration of toxic substances in the water standardized to MPC), the critical levels of water contamination was determined. The dose–effect dependencies were plotted for the above biological parameters. The accumulation of toxic metals can also enhance (and, in certain cases, even directly cause) pathologies in fish. Therefore, the relationship between the accumulation of microelements in fish and pathological disturbances in the organs and tissues of fish in polluted the Volga and Ob river's basins was analyzed. The dose–effect dependencies clearly show that total pollution of the Volga River must be significantly decreased, by at least 5–7 times, first for toxic contaminants. The study of the morphofunctional state, histopathology, accumulation of heavy metals and reproductive performance peled (Coregonus peled) of Ob river basins in the northern part of Western Siberia revealed the influence of heavy metal concentrations in fish on its diseases.
These studies have confirmed the high information value of the ecotoxicological approach to the assessment of water quality and ecosystem health, as well as the necessity of establishing more reliable MPC values. Note that ecotoxicological studies were carried out for the Volga and Ob river's basin for the first time, and many important river sections or reservoir areas were not investigated. In this respect, our studies could be considered "screening analysis of the ecotoxicological situation," but at the same time, they substantiate the information content of methodological solutions and the necessity of the continuation of large-scale studies in this field in the future.
The priority to preserve the natural potential (clean water, biodiversity, valuable fish stocks) needs to develop new approaches and complex decisions for improving ecological policy on the industry development territory. Economic and social optimum should be based on the conception of ecological expenditures - determination of the existing and possible damages from pollution and degradation of ecosystems. The main principle for determining the latter is cost of landscapes' re-cultivation, artificial purification of waters and man-made reproduction of fish resources.